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Residents of a high-rise building at Sydney's Olympic Park endured a "frustrating" night while they waited to be allowed back into their homes after a major safety scare.

The occupants of 150 units of a 392 unit complex were evacuated from their homes when an internal wall in the 36-storey Opal Tower failed.

Many residents heard "cracking" noises at the brand new complex and raised the alarm - and a full evacuation followed as authorities scrambled to discover what was wrong.

Fire & Rescue NSW Urban Search and Rescue (USAR) officers and specialist engineers worked with the building designers and building managers throughout the day and into the night to determine the integrity and safety of the affected floors.

"This is a large building and it's critical the safety of the residents comes first," said NSW Police Force Acting Assistant Commissioner Julie Boon. "Each affected floor is being assessed by engineers before we can determine if and when people can go back into their homes.

"It's been a particularly frustrating time for residents and we're very aware they are keen to go home the night before Christmas. Before that happens, police and emergency services need the building designers and engineers to be confident the building is safe to re-enter."

A temporary shelter was set up at the Sydney showgrounds for those residents who had nowhere else to go.

"It will be a long night for these residents," said Assistant Commissioner Boon. "Police and emergency services are also working with the building managers to put contingencies into place for the affected residents, if needed. Our aim is to ensure the safety of everyone involved before allowing residents to return."

Concerns were raised for the Opal Tower on Brushbox Street about 2.45pm, with occupants telling police they heard the worrying noises throughout the morning.

The building has shifted between one and two millimetres as a result of the issue, Police Detective Superintendent Philip Rogerson said.

But there has been no further movement detected on laser monitors deployed by emergency services.

FRNSW is on scene with specialist equipment designed to monitor the building for any more movement. https://t.co/K14jrJhauA